1. Field of the Invention
This invention relates generally to a device for sensing the type of magnetic coating on a magnetic tape for use with a tape recording and/or reproducing apparatus.
2. Description of the Prior Art
Magnetic tapes coated with various kinds of magnetic materials are now commercially available for use with tape recording and/or reproducing apparatus. For example, magnetic tapes are available that are coated with .gamma.-Fe.sub.2 O.sub.3 (gamma-ferric oxide) or with CrO.sub.2 (chromium dioxide). By reason of the different magnetic properties of such tapes, it is necessary that certain characteristics of recording and/or reproducing apparatus, for example, the bias signal applied to the magnetic recording head and/or the equalizing function of a frequency equalizing circuit, be changed to obtain the optimum recording conditions of the apparatus when used with the various types of magnetic tapes. Accordingly, the conventional magnetic tape recording and/or reproducing apparatus is usually provided with a tape selector switch which has to be manually actuated by the operator of the apparatus for obtaining the proper recording conditions for the magnetic tape to be employed. If the operator forgets to manipulate the tape selector switch to the position corresponding to the type of the tape being employed, or if the type of magnetic coating on the tape is not known to the operator, then recording on the magnetic tape may be effected under less than optimum conditions with consequent loss of the desired recording quality.
In order to avoid the above problem, it has been proposed to pre-record a reference signal, for example, with a frequency of 10 KHz, on an initial portion of each magnetic tape, and to provide the tape recording and/or reproducing apparatus with means by which, prior to a regular recording operation of the apparatus, the pre-recorded reference signal is reproduced and the level of the reproduced reference signal is detected as an indication of the type of magnetic coating on the tape, with the detected level of the reproduced reference signal being employed to automatically select the proper bias signal and equalizing function for the tape in question. However, the foregoing proposed arrangement is disadvantageous in that it requires the pre-recording of the tapes with the reference signal and the reproducing of such reference signal by a reproducing operation of the recording and/or reproducing apparatus prior to the commencement of a recording operation of the latter. In the case of tape cassettes, particularly, the reproducing of the pre-recorded reference signal for establishing the type of tape in the cassette is especially troublesome in that it may require the rewinding of the tape to locate the portion of the latter on which the reference signal is pre-recorded.